Graft-versus-host disease develops in mice transplanted with lymphocyte-depleted bone marrow cells from signal-transducing adaptor protein-2 transgenic mice

STAP-2-Derived Peptide Suppresses TCR-Mediated Signals to Initiate Immune Responses

Signal-transducing adaptor protein-2 (STAP-2) is an adaptor protein that contains pleckstrin and Src homology 2-like domains, as well as a proline-rich region in its C-terminal region. Our previous study demonstrated that STAP-2 positively regulates TCR signaling by associating with TCR-proximal CD3ζ ITAMs and the lymphocyte-specific protein tyrosine kinase. In this study, we identify the STAP-2 interacting regions of CD3ζ ITAMs and show that the STAP-2-derived synthetic peptide (iSP2) directly interacts with the ITAM sequence and blocks the interactions between STAP-2 and CD3ζ ITAMs. Cell-penetrating iSP2 was delivered into human and murine T cells. iSP2 suppressed cell proliferation and TCR-induced IL-2 production. Importantly, iSP2 treatment suppressed TCR-mediated activation of naive CD4+ T cells and decreased immune responses in CD4+ T cell-mediated experimental autoimmune encephalomyelitis. It is likely that iSP2 is a novel immunomodulatory tool that modulates STAP-2-mediated activation of TCR signaling and represses the progression of autoimmune diseases.

Signal-transducing adaptor protein-1 and protein-2 in hematopoiesis and diseases

Inflammatory and immune signals are involved in stressed hematopoiesis under myeloablation, infection, chronic inflammation, and aging. These signals also affect malignant pathogenesis, and the dysregulated immune environment which causes the resistance to treatment. On activation, various types of protein tyrosine kinases in the cytoplasm mediate the cascade, leading to the transcription of target genes in the nucleus. Adaptor molecules are commonly defined as proteins that lack enzymatic activity, DNA-binding or receptor functions and possess protein-protein or protein-lipid interaction domains. By binding to specific domains of signaling molecules, adaptor proteins adjust the signaling responses after the ligation of receptors of soluble factors, including cytokines, chemokines, and growth factors, as well as pattern recognition receptors such as toll-like receptors. The signal-transducing adaptor protein (STAP) family regulates various intracellular signaling pathways. These proteins have a pleckstrin homology domain in the N-terminal region and an SRC-homology 2-like domain in the central region, representing typical binding structures as adapter proteins. Following the elucidation of the effects of STAPs on terminally differentiated immune cells, such as macrophages, T cells, mast cells, and basophils, recent findings have indicated the critical roles of STAP-2 in B-cell progenitor cells in marrow under hematopoietic stress and STAP-1 and -2 in BCR-ABL-transduced leukemogenesis. In this review, we focus on the role of STAPs in the bone marrow.

STAP-2 Adaptor Protein Regulates Multiple Steps of Immune and Inflammatory Responses

Signal-transducing adaptor protein (STAP)-2 is an adaptor molecule involved in regulation of several intracellular signaling events in immune cells. STAP-2 contains a pleckstrin homology domain at the N-terminus, an src homology domain in the central portion and a proline-rich region at the C-terminus. STAP-2 also has a YXXQ motif, which is a potential signal transducer and activator of transcription (STAT)3-binding site. STAP-2 influences the STAT3 and STAT5 activity, integrin-mediated T cell adhesion, chemokine-induced T cell migration, Fas-mediated T cell apoptosis, Toll-like receptor-mediated macrophage functions, macrophage colony-stimulating factor-induced macrophage activation, and the high-affinity immunoglobulin E receptor-mediated mast cell activation. This article reviews the current understanding of roles of the STAP-2 during immune and/or inflammatory responses, and discusses possible therapeutic applications of targeting STAP-2 proteins in immune-related disorders.